Summary of Significant Accounting Policies (Components of Self-Insurance Reserves) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Policy Text Block [Abstract]
Self-insurance reserves (undiscounted)	$ 147,664	$ 138,687
Self-insurance reserves (discounted)	$ 137,970	$ 129,437

The undiscounted portion of self insurance reserves as of the balance sheet date.

No definition available.

Name:	orly_SelfInsuranceReservesUndiscounted
Namespace Prefix:	orly_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant